1. The Field of the Invention
The present invention relates generally to a system and method of reducing marking or smearing of printed sheets on sheet-fed printing presses, and, more particularly, to a matte for use on a cylinder in a sheet-fed printing press.
2. Description of Related Art
Marking and smearing of freshly printed sheets during high speed printing operations on sheet-fed printers have historically been troublesome, costly and time consuming problems. Various methods have been employed to effectuate the handling and transfer of freshly printed sheets between printing stations, or between a printing station and a press delivery, without marking or smearing of the printed sheets. These methods have utilized various types of skeleton wheels, cylinders and other mechanical devices.
Skeleton wheels typically attempt to minimize contact with the printed sheet by using projections or serrations. However, some inherent problems associated with the use of skeleton wheels include sliding of the printed sheet over the projections or serrations or damaging of the sheet itself through indenting or dimpling. By contrast, other methods do not attempt to minimize contact with the printed sheet but instead either provide a coating material applied directly to a transfer cylinder or skeleton wheel which acts as an ink repellant or by mounting a covering on the transfer cylinder or skeleton wheel which is itself coated with an ink repellant and which additionally performs a cushioning function.
The drawbacks and shortcomings of these approaches have resulted in increased labor costs and the attendant loss of efficiency (attributed to: complex installations; increased setup time to accommodate varying sheet sizes, and increased time for frequent washing of the transfer cylinders), increased make-ready time, high maintenance requirements and increased waste. Some of these inherent drawbacks and shortcomings of these various methods are more fully discussed in U.S. Pat. Nos. 5,842,412 and 4,402,267.
In a sheet-fed press, the leading edge of a sheet of printable material is guided via a gripper whereas the trailing edge is typically free. During operation, the gripper pulls the leading edge of the sheet of printable material through the space found generally between two cylinders of the press. This space, or gap, between two adjacent cylinders of the press is often referred to as the xe2x80x9cnip.xe2x80x9d High speed operation of a press using such a gripper arrangement results in additional drawbacks or shortcomings generally known by those of ordinary skill in the art of sheet-fed printing. Some of these additional drawbacks or shortcomings include, but are not necessarily limited to, smearing or marking of wet images, dot distortion, print length difference between one print station and another during transfer within a print output device and xe2x80x9cslap-outxe2x80x9d of the trailing edge of a printed sheet of material.
Slap-out occurs due to a combination of factors, including but not necessarily limited to the trailing edge of the sheet being free, the tendency of the printed sheet to return to a flat or straight position, and the path of the trailing edge through the nip being defined as something other than tangentially between the two cylinders; i.e., since the surface on which the sheet travels is cylindrical and since the opposing surface is also cylindrical, there exists a path between the two surfaces located at the nip which would be simultaneously tangential to both opposing cylindrical surfaces. Were the sheet to travel along this tangential path, there would be no associated problem of slap-out no matter how fast the press was operated. However, since the actual path of the printed sheet is never along this tangential path, the problem of slap-out becomes prevalent and increases with press speed and the degree to which the printed sheet must alter its course from the tangential path.
Therefore, a need exists for an improved device and method to reduce smearing or marking of wet images, dot distortion, print length difference between one print station and another during transfer within a print output device and xe2x80x9cslap-outxe2x80x9d of the trailing edge of a printed sheet of material.
In one embodiment, an apparatus for facilitating handling of sheets in a sheet-fed printing press includes a matte that is mountable on the transfer cylinder. The matte has at least one inflatable pocket for cushioning sheets of printable material as they are passed through the nip. At least one valve arranged to be in fluid communication with the inflatable pocket may be provided for controlling a quantity of fluid in the inflatable pocket. The cushioning provided by use of such an apparatus reduces smearing or marking of wet images, dot distortion, print length difference between one print station and another during transfer within a print output device and xe2x80x9cslap-outxe2x80x9d of the trailing edge of a printed sheet of material.
In another embodiment, a plurality of inflatable pockets located at locations spaced along the long axis of the matte may be included to provide for increased control over various sheet sizes. Additional control over various sheet sizes may be obtained by including a plurality of valves to independently operate each of the inflatable pockets. Ease of installation and removal is accomplished by incorporated mounting holes along the long axis of the matte. Alternatively, the matte may be arranged on the cylinder by adhesively bonding (tape or glue) the matte to the surface of the cylinder or by arranging the matte on the cylinder with VELCRO hook and loop fasteners.
In another embodiment of the present invention, the transfer cylinder is adapted to receive at least one inflatable tube directly onto the outer surface of the transfer cylinder. At least one valve arranged to be in fluid communication with the inflatable tube may be provided for controlling the quantity of fluid in the inflatable tubes.
A plurality of inflatable tubes may be arranged onto the outer surface of the transfer cylinder and at a plurality of locations along the transfer cylinder""s length in order to provide increased control over various sheet sizes. Additional control over various sheet sizes may be obtained by including a plurality of valves for independently controlling the quantity of fluid in each of the plurality of inflatable tubes.
In yet another embodiment, a plurality of grooves are provided in the outer surface of the transfer cylinder extending along the circumference of the transfer cylinder. A pliable membrane is then arranged onto the transfer cylinder and is sealingly attached to the outer surface of the transfer cylinder so as to form sealed cavities. In order to reduce the sealing area, the pliable membrane may be sealingly attached at the outer periphery of each groove, or anywhere from the outer periphery of one groove to a point on the outer surface of the transfer cylinder that is halfway to the next adjacent groove. The pliable membrane may also be sealed to the entire exposed surface of the transfer cylinder as well. Sealing may be effectuated using either an adhesive (tape or glue) or a mechanical sealing means such as an O-ring.
At least one valve arranged to be in fluid communication with the sealed cavities may be provided for controlling the quantity of fluid in the sealed cavities. A plurality of grooves spaced at locations preferably along the long axis of the transfer cylinder resulting in a plurality of sealed cavities may be provided for increased control over various sheet sizes. Additional control over various sheet sizes may be obtained by including a plurality of valves for independently controlling the quantity of fluid in each of the plurality of sealed cavities.
In another embodiment of the invention, a compound matte including at least two mattes is mountable on a cylinder of a sheet-fed printing press. The compound matte includes a first matte and a second matte, each matte having at least one inflatable pocket for cushioning sheets of printed material as they are passed through the first and second cylinders. The second matte is arranged on the first matte and the second matte has openings adapted to allow the at least one inflatable pocket of the first matte to pass when it is inflated.
The invention also includes the method of fabricating a matte having at least one inflatable pocket for facilitating handling of sheets in a sheet-fed printing press. The method includes the steps of selecting an appropriate material and forming the matte with at least one inflatable pocket using means suitable for the chosen material.
Additionally, the invention also includes the method of facilitating handling of sheets in a sheet-fed printing press which includes arranging a matte with at least one inflatable pocket onto the transfer cylinder, selecting a printed sheet size to be fed through the press, actuating at least one valve for controlling the quantity of fluid in the inflatable pocket in accordance with the sheet size selected and operating the sheet-fed printing press so as to cause the printed sheet to be passed through the nip.
The accompanying drawings illustrate certain embodiments of the invention.
FIG. 1a is a cross-sectional view depicting a general overview of a printing system with a matte arranged on a transfer cylinder in accordance with one embodiment;
FIG. 1b is an enlarged view of a xe2x80x9cnip,xe2x80x9d or gap, between the transfer cylinder and the impression cylinder;
FIG. 2 is a plan view of the matte of FIG. 1b illustrating the general configuration;
FIG. 3a is a plan view of the system of FIG. 1b in operation depicting two different sheet sizes;
FIG. 3b is a detailed view of that portion of FIG. 3a indicated by the dashed circle depicting operation of the system with one sheet size and the corresponding pockets inflated;
FIG. 3c is similar to FIG. 3b except that a different sheet size is depicted with corresponding pockets inflated;
FIG. 4a is a cross-sectional view of an alternative embodiment wherein inflatable tubes are arranged directly onto the transfer cylinder via grooves in the outer surface of the transfer cylinder;
FIG. 4b is a cross-sectional view of another alternative embodiment wherein the inflatable tubes are adapted to be arranged directly onto the existing outer surface of the transfer cylinder without the need for grooves;
FIG. 5a is a front elevation view of a further alternative embodiment which has a pliable membrane mounted on a transfer cylinder, the transfer cylinder having grooves in its outer surface so that the pliable membrane and the grooves form sealed cavities;
FIG. 5b is a plan view of the pliable membrane depicted in FIG. 5a. 
FIG. 6 is a cross-sectional view taken along the line 6xe2x80x946 in FIG. 5a illustrating the pliable membrane arranged on the transfer cylinder;
FIG. 7 is a cross-sectional view taken along the line 7xe2x80x947 in FIG. 5a illustrating both activated and deactivated sealed cavities;
FIG. 8 is a cross-sectional view taken along the line 7xe2x80x947 in FIG. 5a illustrating an alternative sealing means for the embodiment of FIG. 5a; 
FIG. 9 is a plan view depicting a compound matte which uses more than one matte arranged one atop the other;
FIGS. 10 and FIG. 10B are a plan view depicting a general overview of a printing system utilizing the compound matte of FIG. 9; and
FIG. 11 is a plan view of the compound matte of FIG. 10 with the inflatable pockets of each individual matte corresponding to the non-print areas of the printed sheet of material inflated.